Answer:
Water
Step-by-step explanation:
In simple words, the volume of a cell refers to the amount of water it contains.
In eukaryotic cells may change their volume according to the effects of either the loss or gain of water. Furthermore, these changes in cell volume are extremely important as they work as a signal for different cell processes such as migration, proliferation, or death.
Therefore, the change of cell volume is principally due to the loss or gain of water.